1. Technical Field
The present invention generally relates to ice formation on aerodynamic surfaces and in particular to icing on airplanes. Still more particularly, the present invention relates to removal of ice formed on the wings of airplanes.
2. Description of the Related Art
A big problem associated with airplanes is wing icing. Frequently, there are incidents related to wing icing on commercial aircraft. Excessive ice on wings endangers the aircraft and its passengers because the ice reduces the airfoil efficiency of the wing. Methods for dealing with ice adhesion on aircraft vary, though most techniques involve some form of scraping, melting or breaking. For example, the aircraft industry utilizes a de-icing solution such as Ethyl Glycol to douse aircraft wings to melt any ice accumulation. The process is both environmentally hazardous and costly. Some aircraft have permanently installed de-icing mechanisms such as a rubber xe2x80x9cbootxe2x80x9daligned along the leading edge of the aircraft wing. The tube is inflated during flight or on the ground whenever icing conditions warrant. This action causes any ice accumulation to break and fall off. Jet aircraft may redirect engine heat onto the wing so as to melt the ice or use heating elements to melt the ice.
Propeller driven aircraft are unable to duct heat to the wing surface and rubber boots on the leading edge of wings are not aerodynamically efficient. Also, de-icing costs are extremely high, at $2500-$3500 per application, and depending on conditions, they could be applied up to ten times a day on some aircraft.
Therefore there exists a need to provide an apparatus and method to efficiently and automatically remove ice from aircraft wings. It would further be desirable to remove ice without the need for chemicals, boots or heating elements.
A dielectric coating is applied to a surface that is prone to icing. Ice detecting sensors are deployed over the surface that is in danger of excessive icing. When sensors detect the presence of ice, a charge opposite that of the ice coating is automatically applied to the surface beneath the dielectric coating. Since ice in its natural state is a negatively charged substance, an identical, negatively charged surface repels or loosens the ice.
Ice has certain physical properties which allow the present invention to selectively modify the adhesion of ice to conductive surfaces. First, ice is a protonic semiconductor, a small class of semiconductors whose charge carriers are protons rather than electrons. This phenomenon results from hydrogen bonding within the ice. Hydrogen bonding occurs because the hydrogen atoms of water molecules in ice share electrons with an oxygen atom. Thus, the nucleus of the water molecule - uniquely a single proton remains available to bond with adjacent water molecules.
Similar to typical electron-based semiconductors, ice is electrically conductive. While this electrical conductivity is generally weak, the conductivity can be altered by adding chemical agents that donate or accept extra charge-carrying particles, i.e., protons in the case of ice. Another physical property of ice is its xe2x80x9cevaporability.xe2x80x9d Evaporability of a substance is a function of vapor pressure at the substance surface. In most materials, vapor pressure drops rapidly at the liquid-to-solid interface. In ice, however, there is virtually no change in vapor pressure at the liquid-to-solid interface. The reason for this is that the surface of ice is covered with a liquid-like layer (xe2x80x9cLLLxe2x80x9d).
The LLL has important physical characteristics. First, the LLL is only nanometers thick. Second, it ranges in viscosity from almost water-like, at temperatures at or near to freezing, to very viscous at lower temperatures. Further, the LLL exists at temperatures as low as xe2x88x92100 degrees centigrade. The LLL is also a major factor of ice adhesion strength. The LLL functions as a wetting substance between the surfaces--the principle behind almost all adhesives--and substantially increases the effective contact area between the surfaces. This increase in contact area strongly affects ice adhesion.
Generally, water molecules within a piece of ice are randomly oriented. On the surface, however, the molecules are substantially oriented in the same direction, either outward or inward. As a result, all their protons, and hence the positive charges, either face outward or inward.
While the exact mechanism is unknown, it is likely that the randomness of water molecules transitions to an ordered orientation within the LLL. However, the practical result of the ordering is that a high density of electrical charges, either positive or negative, occurs at the surface. Accordingly, if a charge is generated on the surface coming in contact with ice, it is possible to selectively modify the adhesion between the two surfaces. As like charges repel and opposites attract, an externally applied electrical bias to the surface that matches that of the charge occurring in the LLL reduces the adhesion between ice and the surface.
The present embodiment provides a power source connected for applying a DC potential across a dielectric coating formed on the surface. When ice forms on the dielectric coating, a charge is set up by the ice that is opposite to that of the surface beneath the dielectric. Sensors detect the ice formation and cause the power source to reverse polarity, which reduces the adhesion of the ice to the surface.
The above as well as additional objectives, features, and advantages of the present invention will become apparent in the following detailed written description.